sync: Include prereleases when ignoring
sync: Include prereleases when ignoring

When calculating the list of ignored packages include also pre-releases.
This is needed, because on Python 2 environment Prequ depends on
backports.tempfile and backports.weakref and their latest released
versions are pre-releases (1.0rc1).

suutari/prequ,suutari/prequ,suutari-ai/prequ